Flange stresses - the basics

[MikeG7]

I'm having trouble understanding "the basics" regarding flange stresses, specifically w.r.t tangential stresses with the Taylor Forge method. Often it seems tangential stress component is the largest of compared to radial and longitudinal stresses. My understanding is tangential stresses are in the direction of the hoop, the radial is outwards (or inwards) and the longitudinal is in the line of the axis. What confuses me is that, if I think about a flange being bolted up, I imagine it twisting or bending in the longitudinal direction as the bolts try and pull the 2 faces closer (in the case of a raised face where there is a gap between the faces unlike an "o" ring face seal where the faces are initially in contact except for the soft gasket). My logic is that I also expect radial and tangential stress components mainly because of poisson ratio where, like for example if you press down on an elastic materials block on a table, you also get stresses in the plane of the table in all directions but those are secondary.
Or am I misunderstanding the basics?
Thanks,
Michael

 

[TGS4]

You're misunderstanding the basics. Try Roarks and annular rings in bending.

 

[MikeG7]

Could you be a bit more descriptive please? Yes, I've looked there but what am I looking for that explains this? I understand what Tangential stresses are, I just don't understand why tightening up a flange causes tangential (= circumferential = hoop) stresses?

 

[prex]

When you try to have a ring rotate about its circumferential center line, half of the section goes towards outside and the other half towards inside. The part that displaces towards outside undergoes an elongation and thus tension stresses, the opposite of course the other half. So the section is under bending and displays tangential stresses.

prex
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